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1352875 
Journal Article 
Competitive sorption-desorption kinetics of arsenate and phosphate in soils 
Zhang, Hua; Selim, HM 
2008 
1 
Soil Science
ISSN: 0038-075X
EISSN: 1538-9243 
173 
1 
3-12 
WOS:000252462100002 
The competition between arsenate (AsO4-3) and phosphate
(PO4-3) on mineral surfaces has the potential of increasing arsenic mobility and bioavailability
in the soil and water environment. In this study, kinetics of competitive sorption of ASO(4)(-3)
and PO4-3 in three soils was investigated in batch systems by simultaneously introducing the
ligands at different molar ratios. Adsorption was carried out at different retention times, and
release was investigated using successive dilutions after adsorption. Nonlinear sorption
isotherms of ASO(4)(-3) and PO4-3 were observed for all soils. Rates and amounts of AsO4-3
adsorption were significantly reduced when PO4-3 concentrations in the soil solution increased.
In addition, the relative sorption preference of AsO4-3 and PO4-3 did not exhibit changes with
reaction time. Desorption and sequential extractions results indicated that a significant amount
of AsO4-3 was irreversibly retained by all soils. Kinetic retention data of AsO4-3 and PO4-3 were
successfully described using a mechanistic multireaction model that accounted for competitive
retention. This study indicates that competition of AsO4-3 and PO4-3 for adsorption sites should
be considered in models predicting arsenic release from soils receiving high phosphorus inputs. 
arsenic; phosphate; competitive adsorption; kinetic retention; multireaction model